1. Field of the Invention
This invention is in the field of rocket motors. More particularly, the invention relates to a new solid propellant motor and method of making same.
2. Description of the Prior Art
The concept of an end burning solid propellant grain can be traced to the early days of rocketry. The jet assist takeoff, or JATO units, developed in this early period for aircraft utilized end burning solid propellant charges. The propellant used for these applications was a black powder pressed into and filling a rocket chamber under very high pressure in order to insure consolidation and reliable firings. Upon storing and/or temperature cycling, however, the motors tended to blow up in unpredicatable fashion. The problem of cracking or shrinkage pull-away of the propellant charge was eventually solved by replacing the black powder with a softer, less brittle propellant, such as one based on potassium perchlorate as an oxidizer dispersed in an amorphous matrix of asphalt. The elongation of this type of propellant was significantly better than the plain powder charge so that tension stresses on the burning charges were less severe. However, there were still motor blow-ups and an extensive research and development effort was required to adapt the newer form of the propellant to an end burning configuration. This was accomplished by forming the propellant into cartridges which in effect were cylinders that were molded undersized, inhibited on all lateral surfaces except one end by a suitable material to prevent burning on those specific surfaces, and tape-wrapped on all inhibited surfaces before being inserted as a free standing element into the rocket chamber. A separate trapping mechanism was utilized to keep the cartridge disposed, and properly constrained for handling, within the chamber or housing. Eventually, utilizing this concept, thousands of JATO type units were produced. In time, the asphalt matrix was replaced by a resin system but the cartridge form continued to be utilized as the propellant elongation was relatively low, on the order of 3 to 5%, while its modulus was relatively high, about 15000 psi.
Eventually, a new design concept evolved relating to a case bonded radial burning charge. The propellant charge was directly bonded to the case and burned in its central axis perforation radially outwardly along its entire length. This concept was developed more and more for military applications where high-performance radial burning systems were required. Most of these applications tended to be high thrust, short to medium burning time operations, which were well suited to the radial burning design. As propellant technology advanced and propellants became more rubber-like, their elongations eventually reached levels of 20, 35 and sometimes as high as 50% in high performance propellants. These propellants were well suited for the radial burning case bonded concept. Because of a special interest in polymer and propellant work, there had been developed a class of propellants with elongations as high as 150% but these were still being utilized for radial burning applications. Thus in the field of endeavor at the time of the invention, there were few requirements for a case-bonded end-burning motor, since the radial burning concept fulfilled most of the existing needs and it was the prevailing opinion, based on past experience, that such an end-burning design could not succeed.